太湖流域降雨和湖水酸根阴离子长期变化及其环境意义

摘要

To explore long-term trends of acid anions in the rain water in Lake Taihu watershed, the lake water and their environmental implications, the variation characteristics, sources and the relationships of SO42-, NO3- in the rain water and the lake water were studied via historical data collection and sampling analysis. The results indicated that SO42- in the rainwater showed a significant decreasing trend since 1990 s with an annual average decrease rate of 0.28 mg/ (L·a), and the NO3-showed a significant increasing trend with an annual average increase rate of 0.05 mg/ (L·a), which suggests an aggravating trend of nitrogen pollution in the rain water. In contrast, SO42- in the lake water showed a significant increasing trend with an annual average increase rate of 1.24mg/ (L·a), and the NO3-showed a significant decreasing trend with an annual average decrease rate of 0.02 mg/ (L·a). During the past 30 years, the ratio of SO42- /NO3-in Lake Taihu water continuously increased, much higher than that of the rain water. The research indicated that the acid deposition caused by SO2 emissions in the watershed was mainly responsible for the increased concentration of SO42- in the lake water. However, the nitrogen oxides emissions did not cause an increase concentration of NO3-in the lake water, indicating that Lake Taihu watershed plays a significant role in the retention of nitrogen deposition, while the lake water is an important sink for sulfate deposition. The regional nitrogen deposition has an important impact on Lake Taihu water eutrophication. It is of great significance to prevent the acidification and eutrophication in Lake Taihu via comprehensive management of acid emissions in Lake Taihu watershed.%为揭示太湖流域降雨和湖水酸根阴离子长期变化特征及环境意义, 通过历史数据收集和采样分析, 对太湖流域降雨和湖水中的SO42-、NO3-变化特征和来源进行了研究.结果表明:自1990s以来太湖流域降雨中SO42-呈显著下降趋势, 年平均下降率为0.28 mg/ (L·a); NO3-浓度却呈显著上升趋势, 年平均增长率为0.05 mg/ (L·a), 降雨中氮污染呈现加重的趋势.与之相反, 湖水中SO42-呈显著上升趋势, 年平均增长率为1.24 mg/ (L·a); NO3-浓度却呈显著下降趋势, 年平均下降率为0.02 mg/ (L·a). 30年以来, 太湖水体SO42-/NO3-比值不断升高, 远高于降水SO42-/NO3-比值.研究认为:流域SO2排放引起的酸沉降是湖水SO42-浓度增长的最重要原因, 但氮氧化物排放并未引起湖水NO3-浓度升高, 说明太湖流域对大气沉降的氮氧化物有滞留作用, 而太湖水体是流域大气沉降硫酸盐的重要汇.综合治理太湖流域酸性物质排放对防止太湖水体酸化和治理富营养化都具有重要意义.